A gas turbine engine may be used to supply propulsion power to an aircraft. In addition to providing propulsion power, an aircraft gas turbine engine may also be used to supply either, or both, electrical and pneumatic power to the aircraft. For example, in the past some gas turbine engines include a bleed air port between the compressor section and the turbine section. The bleed air port allows some of the compressed air from the compressor section to be diverted away from the turbine section, and used for other functions such as, for example, main engine starting air, environmental control, cabin pressure control, and/or hydraulic system reservoir pressurization.
More recently, however, aircraft gas turbine engines are being designed to not include bleed air ports. This is in response to a desire to more fully utilize electrical power for main engine starting air, environmental control, and cabin pressure control. Thus, instead of using engine bleed air to support these various functions, the high pressure turbine may be used to drive one or more electrical generators to supply electrical power to support these functions.
Nonetheless, many aircraft still include various hydraulic systems and components. Such hydraulic systems and components may include one or more hydraulic fluid reservoirs. In many instances, these hydraulic fluid reservoirs may need to be pressurized to provide sufficient net positive suction head in order to prevent cavitation of the hydraulic pump (or pumps) in the hydraulic system. As was alluded to above, engine bleed air has been used in the past to pressurize hydraulic fluid reservoirs in at least some aircraft hydraulic fluid systems. However, by designing engines without bleed air ports, this source of air is unavailable to provide this function. Although other sources of air are available on an aircraft that is not configured to use engine bleed air, these sources of air may not be pressurized to a sufficient magnitude to adequately pressurize the hydraulic fluid reservoirs. Moreover, it may not be desirable or efficient to utilize the electrical power generated by the aircraft gas turbine engines to compress the air to a sufficient magnitude.
Hence, there is a need for a system that can pressurize the air from relatively low pressure air sources to a magnitude sufficient to pressurize one or more hydraulic fluid reservoirs, without relying on electrical power to do so. The present invention addresses at least this need.